The invention relates to a device for connecting the sheath of an electric winding to a ground conductor and to a magnetic levitation railway (maglev train) equipped therewith.
With magnetic levitation railways having long-stator linear motors, a long-stator is provided alongside a guideway, into the grooves of which a three-phase alternate current winding is inserted, which for example consists of a copper or aluminum cable and an insulating layer surrounding it. Since differences in voltage occur due to inductive effects in normal operation along the windings and because currents thereby caused may flow, it is known (DE 30 06 382 C29) to provide the windings with an additional outer sheath made of an electrically isolating plastic material being made at least partly electrically conductive with carbon black, graphite, a copper mesh or otherwise in order to discharge these and other electric currents, to ensure hazard protection on contact and for other reasons, and to connect this sheath in the area of each groove to a ground conductor extending alongside the long-stator. To ensure that small transitional resistances are obtained between the sheath and the ground conductor, it is furthermore well known practice (DE 196 20 222 C2) to connect the winding sheath to the ground conductor by means of devices which consist of sleeves partly surrounding the windings, are inserted into the grooves of the long-stator and comprise connecting elements for the ground conductor. Thereby it is intended on the one hand to establish a comparably large contact between the sheath and the sleeves, while the connecting elements on the other hand are intended to allow for a simple connection to the ground conductor. For avoidance of corrosion, the sleeves and the connecting elements are made of stainless steel.
The ground conductors hitherto consist of a well conducting material, e.g. copper. They are connected at optional points and optionally frequently to the ground potential and provided with a conductive plastic sheath like the alternating current windings to provide corrosion and contact protection.
In practical use of magnetic levitation railways, two essential weak points have shown up in the described devices. On the one hand it was found out that the plastic sheath of the ground conductor was scorched through at numerous points after a longer period of operation. Such scorched points indicating thermal overloads are not tolerable. On the other hand, fire and/or carbonization points also occur in the sheath of the long-stator winding itself, whereby the sheath gradually becomes brittle and begins to dissolve. This is not tolerable either.